Colorado has revoked waivers from as many as 72 public drinking-water systems and is now requiring chlorine treatment of most public supplies as part of the response to a salmonella-poisoning epidemic that ravaged Alamosa last year.

A Colorado Department of Public Health and Environment report released Wednesday confirmed earlier suspicions that a decrepit infrastructure allowed deadly bacteria from animals to invade Alamosa's 320,000-gallon Weber Reservoir.

Still, the report said, had the city used chlorine to disinfect its water supply, the bacteria might not have grown. That finding has now prompted the state to redouble its efforts to require chlorine treatment in most places where the public shares a water supply.

The problems that led to the epidemic were first seen in 1997, when an inspection found cracks and other signs of decay in the corners and walls of a ground-level water reservoir. But the report found that the city made recommended changes.

"There is no evidence that the recommendation to routinely clean and inspect the reservoir was addressed by the city in subsequent years," the state reported.

Ten years later, the department sent an inspector to check Alamosa's water system. "A thorough inspection of the Weber Reservoir did not take place," however, the report said, after the city told the inspector that the reservoir would be separated from its drinking-water system soon.

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When asked what could have prevented the epidemic, state drinking-water program manager Ron Falco, the report's co-author, answered, "Chlorination."

Alamosa had been exempted since 1974 from a state requirement to treat drinking water with chlorine, which kills salmonella bacteria.

The state report concludes that salmonella bacteria from animal feces probably got into Alamosa's drinking-water supply early in March 2008 and infected the entire city water system during the next week.

"Perfect storm" of woes

That caused the worst waterborne-disease outbreak in the U.S. since 2004. In Alamosa, a city of 8,900, an estimated 1,300 people may have been ill, including 40 percent of its infants. State officials identified 442 cases of "probable salmonella infections," and one man died.

In the aftermath, the state accelerated its review of 126 public-drinking-water systems — in towns, school districts, mobile-home parks, campgrounds — that had been exempted from chlorination in Colorado. Seventy-two chlorination waivers have been canceled, including Alamosa's. Others are under review.

The Alamosa report cited "a perfect storm of multiple defects" in the city water system at the time of the outbreak: the chlorination waiver, poor maintenance, incorrect bacteria testing and inadequate supervision by a chronically short-staffed state drinking-water program.

After the enclosed, ground-level reservoir was drained during the epidemic, the crew entering it found holes "through which daylight could be seen" and waded through layers of sediment estimated at 12 to 18 inches deep in places. It had not been drained and cleaned in 24 years.

Inspectors also found:

• There were 145 gallons of sediment and missing bolts in a city water tower of unknown age, possibly built in the 1930s. The bolt holes could have exposed the tower's water to bird feces.

• Two mortuaries and a meat-packing and restaurant property posed an "extreme hazard" that water from their buildings could back into the public supply.

• Alamosa's tests for coliform bacteria in its water had not complied with federal requirements for diverse sampling in the distribution system.

Warm water pumped in

Don Koskelin, Alamosa's public-works director, said the city is working to correct all the reported deficiencies, "to make darn sure it can't ever happen again."

In Alamosa, the underground water pumped into its reservoir was warm — 75 degrees or more, a welcome environment for bacteria. Its warmth also attracted wildlife, birds and small mammals to the top of the fenced reservoir in winter. A tiny bit of salmonella-infected feces invading its holes or cracks "most likely" caused a massive disease outbreak, the report concluded.

"Millions, or even billions, of germs can be released in the feces of an infected human or animal," the report said, and a child can be infected by as few as 10 to 100 salmonella organisms.

Some towns that lost their chlorination waivers after Alamosa's outbreak are complying with state orders reluctantly.

"We had quite the round with them over that," said Mark Brown, city superintendent in Holyoke. "We know we have good-quality water. We run our system correctly."